Whats the easiest way to determine if a user is online? (PHP/MYSQL)

Question

Is there a way I can piggy back sessions to know if the user is online?

I.e: use logs on, I set a $_SESSION variable, user times out- cookie Garbage collector update

Answer 1

Here's a way on how to get the difference between two dates from a database in minutes, then check for the difference and set the online/offline status.

$query = 'SELECT * FROM Users';
$result = mysqli_query($mysqli, $query);

foreach($result as $user){
    // date from the database
    $dbLastActivity = date("d-m-Y h:i:s a", strtotime($user['lastOnline']));
    // date now
    $now = date("d-m-Y h:i:s a", $date);

    // calculate the difference
    $difference = strtotime($now) - strtotime($dbLastActivity);
    $difference_in_minutes = $difference / 60;

    // check if difference is greater than five minutes
    if($difference_in_minutes < 5){
        // set online status
        $updateStatus = 'UPDATE Users SET Status="online" WHERE lastOnline="'.$user['lastOnline'].'"';
    } else {
        // set offline status
        $updateStatus = 'UPDATE Users SET Status="offline" WHERE lastOnline="'.$user['lastOnline'].'"';
    }

    // check if mysqli query was successful
    if (!$mysqli->query($updateStatus)){
        printf("Error Message %s\n", $mysqli->error);
    }
}